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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

Handling should be better because of the stiffer springs there should be less body roll. I would think your cornering speeds should go up.

I don't think it should hurt resale value too much. There are definitely quite a few people out there who like lowered cars. Some people may steer clear because they prefer stock ride height, but there should be enough who prefer lowered cars to balance it out.

If you have the cash coilovers might be a good way to go as you won't be locked into one ride height and depending on what set up you go with you may have various dampening adjustments too.

The really hard part of your question is regarding "bone jarring" or how bad the ride will be as that is so subjective. What might be bone jarring to one person might just be firm to someone else. Also some people are willing to put up with a harsh ride because having a slammed car is more important than the ride characteristics.

You might try posting in your regional forum and see if you can find someone who will give you a ride in their e39 with the setup you are considering. If you can find that it would be the best way to go as they you can get an idea of what the suspension feels likes before you buy and install it on your car.

Also if you go with H&R race do you know what dampers you are going to use?

I've been running H&R springs for the past 6 years on my E39 Touring and for 4 years on my E34 prior to that and I've been extremely happy in both cases. I've been told that on oem standard shocks (non sport) the max to lower is around 30mm as any lower means shortened (sport) shocks would be required. As you already have the Sport shocks, you can go a bit lower to perhaps 40-50mm. To answer your questions

1. There will be an increased harsher ride of perhaps 10-15% - there's nothing really you can do to counter that. Other cheaper springs would possibly be 20-30% or more harshness which perhaps would be the negative difference many owners wouldn't want.
2. Handling is much improved! lower centre of gravity and higher quality springs and their characteristics mean you'll most likely really love the car's increased cornering capabilities and overall ride quality and compliance.

3. How often do you drive at 130+ mph? aside from that, the car's drive, handling, ride and feel will be all improved at 0-whichever speed you wish to drive

4. Lower re-sale value ? - the purists will say yes. In the real world, it's extremely marginal as there's no hard and fast set rule as to how much a car is worth when you talk actual 'selling prices' as opposed to asking prices.

5. Consider which wheels you wish to run compared to the amount of lowering you want. Looks like you have 17 inch Style 66's in your picture. Going too low on 17's makes the wheels look tiny, so I'd say go to 18's but preferably 19's.

Lastly, everyone is different and will put up why to or not to lower etc etc, but it's down to you. This forum is particularly 'oem' biased and those of us who run more modified examples do provide real world experience which often pushes the misconceptions to the side. My E39 is a daily driver, and I've often carried my dog in it, and also family and friends who have not got one clue that it's lowered and having ever mentioned it's a bad ride. In short, the better quality or higher end of products you go the better ride and quality you'll get.

I've got H&R 50464 springs along with Koni FSD's and M5 roll bars front and rear.
The ride isn't bone jarring at all. Handling is superb even at speeds greater than you mentioned. The twisties are even more fun, but at a bit slower speed, but still faster than the OEM suspension can take.

I wouldn't worry about re-sale value. It's already rock-bottom low. First thing people look at a used car are tires, and if they're worn, they start haggling about that. Besides, if you think selling, I wouldn't even change the springs/shocks.

Honestly installing H&R's is not going to make a huge difference in ride height or quality.
A little lower, a little stiffer.

Most people wont even be able to tell the difference.
Or at least that's my perspective, my e39 is dropped over three inches on stiff coilovers so sport springs aren't a big deal from my point of view..

A word of advice if you have 110k on your shocks and your thinking about replacing the springs just go ahead and replace your shocks, if they aren't gone yet they're headed there fast, and pulling struts isn't something you want to do often, trust me. Billstein HD's are cheap(ish) and nice.

Best 540i I've ever seen, extremely clean and classy, not dumped and tacky. Coilovers will help ALOT, believe me the difference between springs and a full set of coilovers is night and day. Don't go get some chinese coilovers though, at least get the KW Variant 1. They're pricey but hey you gotta pay to play. I would also focus on power mods if I were you and some better brakes would be nice, never underestimate braking importance . Most of all though if you really want alot of grip get good tires, people forget that at the end of the day everything the car does, everything it aims to do is through the tires, that's the last contact point to the road. I would get Toyo R888s but of course their rain performance is crap and they wear out fast but for ultimate street tire grip and performance the R888s are second to none.

By this time you will have spent thousands on the 540i which makes you think is it worth it and why not just get a better car for the money you'll spend.